This project is an extension of previous work directed toward the study of noninvasive methods to determine spatial and temporal relationships existing between tissues of clinical interest. The approach involves in vitro modeling of promising systems and the development of prototypes suitable for clinical evaluation. Recent work has focused on studies directed toward development of a versatile computerized dental radiographic system designed to be used both fluoroscopically and off-line to produce images which can be subtracted to show small changes in tissue occurring over long intervals of time, and combined in ways permitting tomosynthetic display of specific slices of the teeth and jaws. An all-electronic prototype is being fabricated which couples an x-ray source capable of moving its focal spot to different positions in a circular orbit under the control of a digital computer. This process takes less than a second to produce eight discrete pulsed exposures which are recorded in real time using one of three different video-based detector systems currently under development; a pin-diode array, a solid-state chip based on D-RAM technology, and a tiny image-intensified optical system fiber-optically coupled to a miniaturized video camera. Significant progress has been made in the development of related soft-ware. Data form controlled studies now confirm that image subtractions produced form appropriately weighted projection data are compromised less by differences in projection geometry than comparable data produced using nearest-neighbor, control projections. In theory, this opens the door to image comparisons obtained from existing clinical records including the wealth of retrospectively produced periapical radiographs already residing in patient files.